[Dnsmasq-discuss] Different behaviour with "interface=" on two almost identical systems

[Chris Buechler]

On Thu, Mar 28, 2024 at 11:40 AM Chris Green <cl at isbd.net> wrote:

>
> I did try stopping dnsmasq and then nothing was listening on port 53.
> However, just to prove it:-
> root at backup:~# ss -tulpn sport = 53
>
>     Netid State  Recv-Q Send-Q Local Address:Port  Peer Address:Port
> Process
>     udp   UNCONN 0      0            0.0.0.0:53         0.0.0.0:*
>  users:(("dnsmasq",pid=1826,fd=4))
>     udp   UNCONN 0      0               [::]:53            [::]:*
>  users:(("dnsmasq",pid=1826,fd=6))
>     tcp   LISTEN 0      32           0.0.0.0:53         0.0.0.0:*
>  users:(("dnsmasq",pid=1826,fd=5))
>     tcp   LISTEN 0      32              [::]:53            [::]:*
>  users:(("dnsmasq",pid=1826,fd=7))
>

That's the nature of how dnsmasq binds by default. You need two config
lines to actually bind only to localhost:

listen-address=127.0.0.1
bind-interfaces

The listen-address config will make it only reply to queries to localhost,
but doesn't prevent wildcard binding. bind-interfaces makes it bind
explicitly to the listen-address. See the bind-interfaces section of the
man page for details.
https://thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html
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